Electrical stethoscope



July 17, 1956 F. B. zENER ETAL ELECTRICAL STETHOSCOPE Filed Jan. 7,1955` l rraeA/EV.

United States Patent() ELECTRICAL STETHOSCOPE Francis B. Zener, SantaBarbara, and John A. Moseley, Malibu, Calif.

Application January 7, 19.55, Serial No. 480,370

4 Claims. (Cl. 179-1) This invention relates generally to a novelelectrical stethoscope and particularly describes such a deviceincluding a new and unusually effective microphone housing for use witha stethoscope.

In the preferred embodiment of the present invention there is provided amicrophone housed in a body, the output of the microphone being arrangedto be amplified by conventional electrical amplifier means. The outputof the amplifier, in the form of an amplified electrical signal, is fedto a small speaker whose acoustic output is connected to a pair offlexibly mounted tubes terminating in conventional plugs for insertioninto the ears of the user.

Although electrical stethoscopes have been proposed in the past, theyhave been subject to disadvantages in operation and use principallyresulting from the picking up and amplifying of unwanted sounds. Suchsounds are caused, for example, by the microphone or microphone housingrubbing against the clothing or body of a person being examined. By thepresent construction these disadvantages are minimized and virtuallyeliminated. Preferably a microphone with a frequency response of from 40to 6000 cycles per second is employed in the invention and sinceextraneous sounds are excluded as above mentioned, the present inventionis particularly well suited for detecting respiratory, cardiac andperistaltic sounds as well as the fetal heartbeat.

Accordingly it is a principal object of the present invention todisclose a novel electrical stethoscope.

Another object of the invention is to provide an electrical stethoscopewhose construction minimizes the introduction of unwanted extraneoussounds into the system.

A further object is to disclose, in the above apparatus, a microphonehousing consisting of a body having a hollow chamber near one endthereof for resiliently housing a microphone and including in its otherend an impedance-matching section including outwardly flared horncommunicating with the microphone chamber through an aperture formed inthe housing.

A further object of the invention is to disclose an apparatus of theabove character including means for protecting the microphone fromdamage caused by jarring when inadvertently dropped or otherwisemishandled, as well as to acoustically shield the diaphragm of themicrophone.

These and other and allied objects of the invention will become clearfrom a study of the following description of a preferred embodimentthereof taken in connection with the accompanying drawing in which:

Fig. 1 is a diagrammatic layout of a complete elec trical stethoscopeembodying the present invention.

Fig. 2 is a longitudinal sectional view through the microphone housing;and

Fig. 3 is a fragmentary sectional view, on an enlarged scale, taken online III-III of Fig. 2.

Referring now in detail to the drawing there is shown in Fig. l amicrophone housing indicated generally at 2,755,336 Patented July 17,1956 ice connected through a suitable electrical cable 12 to the inputof an electrical amplifier indicated generally at 14 supplied withelectric power through leads 15. The amplifier 14 may desirably includeconventional volume control means 16 and its output is fed throughelectrical cable 18 to the female portion 20 of a detachable plug jackconnection of conventional design.

A small dynamic speaker 22 is provided with an insertable plug 24removably receivable in known fashion in the jack 20. The acousticoutput of the dynamic speaker or transducer 22 is coupled through aresilient sleeve 26 to the yoke portion 28 of a stethoscope. Acousticwaves originated by the transducer 22 and fed to yoke 28 are furtherconducted through resilient sleeve members 3f) to ear tubes 32terminating in inwardly directed earpieces 34. The apparatus justdescribed includes resilient member 36 to hold the component members inposition as indicated and consitutes the well known physicians headpieceor harness for listening to sounds such as heart beats andthe like.

A preferred form of the microphone housing 10 used in the presentinvention is shown in detail in Fig. 2. As there appears, the housingbody 10 is made of rigid material having in its rear portion a hollowchamber indicated generally at 4f), and in its front portion animpedancematching section including an outwardly flared horn indicatedgenerally at 42. Within the chamber 40 there is provided a microphoneindicated generally at 44. The microphone 44 is preferably of thepiezo-electric type, affording good frequency response from therelatively low frequency heart beat sounds to the respiratory andperistaltic sounds of higher frequency.

The chamber 40 is desirably cylindrical in shape and a layer ofresilient acoustic insulation material is provided as a lining for boththe cylindrical side wall of the chamber 40 as well as the majorportions of the end walls defining the chamber. Thus the resilientlining includes a cylindrical portion 46 extending the length of thechamber dii, a disk-shaped portion 48 across the rear end of the chamberand an annular portion 50 across the front end of the chamber. Theresilient members 46, 48 and 5f) may be made of rubber or suitablesubstitute having similar resilient characteristics.

The microphone 44 within the chamber 40 is supported on the cylindricalresilient member 46 and is provided with output leads 56 and 58, theformer lead being grounded at 60 to an access and mounting plate 62coustituting the rear closure member for the microphone chamber and heldin position relative to the body housing by suitable fastening means 64.The end plate 62 includes an aperture 66 therethrough and a conventionalcoupling member 68 is threaded therein and held in assembled relation asby nut 70. The outer portion of the coupling member 63 includes aportion of increased diameter 170 to which may be threadedly connectedthe female portion of a conventional electrical fitting 72. Electricalconnection is thus made between the contacts at 74 and the conductor 5Sis thereby connected to the output lead 76 which is desirably a portionof coaxial cable 12 as indicated.

In the front portion of the housing body 10 the impedance-matchingsection 42 includes outwardly and frontwardly diverging walls 80 whichare convexly formed in an exponential curve of revolution. At the innerend of the curved walls 80 the horn 42 communicates with a restrictedthroat or channel 82 which terminates rearwardly in an aperture 84. Thusthe housing body 10 is provided, in effect, with a. transverse partitiondividing the microphone housing 40 in the rear portion of the body fromthe horn 42 in the front end thereof, and this partition is providedwith the central aperture 84. Desirably the rear surface of thepartition, constituting front wall of the microphone housing chamber 40includes a recessed portion 86 constituting an enlarged air chamberimmediately rearwardly of and in communication with the aperture 84. Themicrophone 44 includes a frontwardly disposed llexible diaphragm 88which is thus exposed to sound waves existing within the air chamber 86.

It will now be understood that the front end of the horn 42 formed inthe housing body 10 and dened by the circular rim 90, may be placed indirect contact with a portion of a persons body near the origin ofsounds to be investigated by means of the present apparatus. The rim 90effectively isolates the microphones diaphragm 88 from sound wavesoriginating elsewhere than the particular area surrounded by the rim 90.The sound waves thereby transmitted into the horn 42 are conductedthrough the throat portion 82 and the aperture 84 into the air chamber86. When the horn 42 is constructed as herein shown and described, bodysounds are thus transmitted into the air chamber 86 and impinge on thediaphragm 88 with a minimum of attenuation, and the resilient mountingof the microphone within the rear portion of the housing body etectivelyisolates the microphone from extraneous sounds or vibrations.

Accordingly' it will be seen that we have provided a novel and usefuldevice by which to receive and make audible various body sounds fordiagnostic purposes. Moditications and changes from the specific formsof the invention hereinabove shown and described as illustrative may bemade without departing from the spirit of the invention, and suchmodifications and changes are intended to be embraced within the scopeof the appended claims.

We claim:

l. An electrical stethoscope comprising: a microphone housing includinga generally tubular body having a front portion provided with anoutwardly directed horn converging inwardly to an axial channel and anenlarged air chamber formed in the body rearwardly of the channel and incommunication therewith and a rear portion provided with a cylindricalmicrophone chamber; a layer of resilient, soundinsulating materiallining said microphone chamber; a microphone within the microphonechamber supported by said layer having a diaphragm exposed to said airchamber; electrical conductors operatively connected to the microphoneand leading outwardly of the housing; amplifier means connected to saidconductors for amplifying signals from said microphone and provided withoutput terminals; an elongated electrical cable connected to said outputterminals; an electroacoustic transducer operatively connected to theother end of said cable; a pair of flexible tubes connected to saidtransducer terminating in laterally spaced ear members; and harnessmeans for resiliently biasing the ear members toward one another.

2. The invention as stated in claim 1 wherein the walls of said horn areconvexly formed in an exponential curve of revolution.

3. In an electrical stethoscope, a microphone housing comprising: a bodyof rigid material having an enlarged cylindrical chamber in its rearportion; a layer of resilient material lining the side wall of saidchamber; a closure means forming an outer rear end wall for said chamberand provided with means for leading an electrical conductortherethrough; a transverse partition intermediate the ends of said bodyforming the front inner end wall of said chamber and provided with acentral aperture therethrough, said front inner end wall having afrusto-conical surface inclined steeply outwardly from said aperture;and an acoustic impedance-matching section formed in the front portionof the body and terminating inwardly in communication with saidaperture.

4. In an electrical stethoscope: a housing made of rigid materiai andhaving front and rear portions, the rear portion being provided with amicrophone chamber formed therein and the front portion including atransverse partition having a small centrally disposed aperture formedtherein, the partition having a rearwardly directed frusto-conicalsurface inclined steeply outwardly from the partition aperture and afront surface constituting an acoustic horn flaring outwardly from theaperture; and a microphone disposed within the chamber including adiaphragm facing said frustoconical surface.

References Cited in the file of this patent UNITED STATES PATENTS1,540,585 Abbott June 2, 1925 1,791,932 Miller Feb. l0, 1931 2,145,449Lockhart Ian. 31, 1939 2,419,471 Thibos Apr. 22, 1947

